From an engineering standpoint I don't know that I would agree that boxer engines are ideal for motorcycles. There are tradeoffs. You get good cooling characteristics from an air cooled boxer twin, but you also have side torque issues...

What side torque issues are we talking about? If you're talking about the chassis yaw torque associated with the relative front-to-rear offset of the cylinder bores, yes, that's an issue, but a pretty minor one. An inline 4 eliminates this by having the 1 and 4 pistons in sync and the 2 and 3 pistons in sync (but 180 degrees out of sync with 1 and 4). The Goldwing's 6-cyl boxer can't fix the problem.

If you're talking about chassis roll torque associated with the crankshaft's torque output, then no. We've had these discussions before, and if the entire driveline is taken into consideration, there is no net torque on the chassis except as relates to crankshaft angular acceleration (which doesn't absorb much of the engine's output unless you're just revving the engine with the gearbox in neutral).

Originally Posted By: Mister_Tee

...and a more complex engine/clutch/transmission arrangement than you would have with an inline.

What is intrinsically more complex about a boxer engine's driveline as compared to a longitudinally-mounted inline four-cylinder, or a transverse-mounted four-cylinder, or any other engine, e.g. Harley's V-twin?